1. Technical Field
The present invention relates to an image display apparatus.
2. Related Art
In recent years, projectors have come into wide use.
In addition to a front projection type projector that is used mainly for business presentation, recently recognition of a rear projection type projector as a form of a large-sized television (PTV: projection television) is growing.
The biggest advantage of a projection type display apparatus is that the projection type display apparatus can provide a screen having the same size as direct view type displays, such as a liquid crystal television or a PDP, with a low cost compared to direct view type displays.
However, as direct view type displays are also becoming cheap, high resolution and performance are required even for projection type display apparatuses.
A projector illuminates light emitted from a light source, such as an arc lamp, onto a light modulation element, such as a liquid crystal light valve and projects light modulated by the light modulation element onto a screen, such that an image is displayed on the screen.
At this time, an image is displayed on the screen but the entire surface of the screen glares.
This is referred to as speckle noise or scintillation, since the phenomenon occurs due to brightness unevenness caused by interference between light beams.
Here, a principle of occurrence of the scintillation will now be described.
As shown in FIG. 15, light beams emitted from a light source 101 are transmitted through a liquid crystal light valve 102 and are then projected onto a screen 104 by a projection lens 103.
The projection light projected onto the screen 104 is diffracted due to a scattering structure of the screen 104, and the diffracted light beams are diffused while moving like two-dimensional waves.
Two spherical waves of the two-dimensional waves strengthen or weaken each other depending on the phase relationship therebetween. As a result, the spherical waves appear as striped patterns (interference fringes) of brightness and darkness between the screen 104 and a viewer.
When the eyes of the viewer focus on an image surface 105 on which the interference fringes occur, the viewer recognizes the interference fringes as scintillation that causes the screen surface to glare.
The scintillation causes a viewer, who desires to watch an image formed on the screen surface, to feel as if a veil, a lace cloth, or a cobweb exists between the screen surface and the viewer.
In addition, since the viewer watches double images including an image formed on the screen and the scintillation and the eyes of the viewer focus on both images, the viewer's eyes can become fatigued.
As a result, the scintillation causes such a large stress that the viewer cannot stand.
In recent years, a new light source that will substitute for a known high-pressure mercury lamp is under development. In particular, the expectation of a laser light source as a next-generation light source for a projector is increasing in terms of energy efficiency, color reproduction, long life, instantaneous lighting, or the like.
However, in the case of projection light that is projected on the screen by the laser light source, extremely high interference occurs since phases of light beams of adjacent regions are equal.
In the case of a laser light source, the coherent length may amount to even several tens of meters. Accordingly, when light beams emitted from the same light source are split and then recombined, light beams combined through an optical path difference shorter than the coherent length cause strong interference.
As a result, scintillation (interference fringes) occurs that is more distinct than that in the case of the high-pressure mercury lamp.
For this reason, particularly in the case of commercial production of a projector using a laser light source, reduction of the scintillation is an indispensable technique.
Japanese Unexamined Patent Application, First Publication No. H11-38512, Japanese Unexamined Patent Application, First Publication No. 2001-100316, and Japanese Unexamined Patent Application, First Publication No. 2006-47422 disclose techniques for reducing the scintillation.
Japanese Unexamined Patent Application, First Publication No. H11-38512 discloses a screen whose diffusion property is optimized and which has a three-layered structure including a diffusion layer, a transparent layer (lenticular lens), and another diffusion layer.
In this case, the random nature of interference spots becomes large due to the diffusion layers that are made complicated.
Therefore, if fine components (interference fringes with low spatial frequencies) increase in spots, light beams are integrated and averaged due to the frame rate at which humans see (hereinafter termed “the afterimage effect”) when a viewer's line of sight moves.
Particularly in the case of motion pictures, since the movement of viewer's line of sight occurs frequently, reduction of the scintillation may be expected.
Japanese Unexamined Patent Application, First Publication No. 2001-100316 discloses a screen in which light beams, an electric field, a magnetic field, heat, or the like are applied to a light scattering layer. In this screen, shape, relative position, or refractive index of light of the light scattering member, contained in the light scattering layer, changes with time.
Thus, the occurrence of scintillation may be expected to be reduced by temporally changing the scattering distribution or phases of scattered waves generated by the light scattering layer.
Japanese Unexamined Patent Application, First Publication No. 2006-47422, an image projection apparatus includes: a laser light source that emits light beams having coherence; a half wavelength plate (polarization control unit) that temporally changes the polarizing direction of the light beams emitted from the laser light source; and an MEMS mirror and a galvano mirror (scan device) that cause the laser beams emitted from the polarization control unit to be scanned in the two-dimensional direction of a scan surface.
In addition, a speckle pattern (speckle intensity) generated in each pixel changes for each frame by rotating the half wavelength plate.
For example, in the case in which each frame is drawn at a frame rate of 60 Hz (sixty number of frames are drawn during one second), each frame which is drawn at every 1/60 second is not viewed by a human. Furthermore, sixty frames are drawn during one second, then intensities of speckle patterns generated in each frame is integrated due to the afterimage effect. Therefore, the speckle pattern occurring at each frame is not viewed. As a result, the images in which the speckles are reduced are drawn.
As described above, by wobbling laser beams emitted from a light source using the polarization control unit or rotating the half wavelength plate so as to change the polarization, speckles of light emitted from a screen are reduced.
However, in the technique disclosed in Japanese Unexamined Patent Application, First Publication No. H11-38512, the scattering state of a final scattering surface is fixed. Accordingly, the phase distribution in the space, in which interference between light beams generated from respective spots on the scattering surface occurs, between a screen and a viewer is also fixed. As a result, even interference spots are viewed as a fixed image.
Therefore, the interference spots do not disappear completely. Particularly in the case of a projector having a highly coherent laser light source, there is little effect of the technique.
In addition, since there is concern that image blurring will occur in the above configuration of raising the light scattering level, it was not possible to realize the original object which was to increase the resolution.
Furthermore, in the technique disclosed in Japanese Unexamined Patent Application, First Publication No. 2001-100316, a large amount of driving energy is needed because the shape, relative position relationship, or refractive index of light scattering member changes.
In addition, in the case of using a driving unit, the efficiency of energy transferred to the scattering layer is low, and vibration, sound, unnecessary electromagnetic waves, and exhaust of heat occurs. As a result, there is concern that comfortable appreciation of images projected on a screen is degraded.
Moreover, in the configuration in which the scattering layer moves in the focus direction, the size of the image changes.
As a result, the position of the border line of the image in the horizontal direction also changes, which is a cause of image blurring.
Furthermore, in the image projection apparatus disclosed in Japanese Unexamined Patent Application, First Publication No. 2006-47422, the polarization of laser beams emitted from the laser light source changes. This is effective for a scan type image display apparatus that scans light in order to project the light.
However, this configuration cannot be applied to image display apparatuses using spatial light modulators (for example, transmissive liquid crystal panel, reflective liquid crystal panel, or DMD).